(a) Field of the Invention
The present invention relates to a method of preparing bio fuel from algal galactan, and more particularly to a method of preparing bio fuel as an alternative to oil fuel, which has high energy density and low hygroscopic property, with a starting material of galactan easily derivable from macroalgae utilizable as marine biomass.
(b) Description of the Related Art
Currently, limited reserves of oil resources and appearance of a new developing country such as China or the like have caused an upsurge in oil prices due to increased demand, and the oil resources are on the brink of being exhausted in the foreseeable future. Further, the oil resources are nonrenewable so that the enormous environmental expenses can be expected based on the international covenant. Accordingly, all countries of the world have made a lot of effort to develop an alternative to the oil resources.
Carbohydrate-based biomass which can be recycled and sustainably used has been on the rise has emerged as the most realistic alternative to such irreversible fossil fuel. With the countries having a large arable land, e.g., the United States, Brazil, etc. as the center, sugar-based substance such as sugar cane or farinaceous-based substance such as corn is used as a starting material and undergoes saccharification and fermentation to industrially mass-produce bio ethanol. Thus, the bio ethanol is used for transportation fuel or the like.
The biomass is broadly divided into a crop system used as food like a sugar system (sugar cane, a sugar beet, etc.), a farinaceous system (corn, a potato, a sweat potato, etc.), and a lignocellulosic system (wood, rice straw, waste paper, etc.) Currently, a polysaccharide carbon source that can be got from the biomass may include starch or sugar got from a crop system supply resource, cellulose that can be got from the woody system supply source, etc. Such polysaccharide substance is got from a pretreatment of a biomass supply source, and the polysaccharide substance such as the starch, sugar and cellulose got from the pretreatment undergoes the saccharification based on hydrolysis and is converted into hexose such as glucose or fructose. Then, the hexose is converted into ethanol and butanol as petroleum-alternative fuel or an alternative material through bio-fermentation.
From the practical use point of the biomass resource, already-industrialized bio ethanol has so low energy content (e.g., about 75% of that gasoline has) that the existing engine has to be inevitably changed in order to use the bio ethanol as single fuel. Further, the bio ethanol is so highly hygroscopic that there is a high risk of corroding an engine or a pipe. Also, since ⅓ of a carbon source is emitted as carbon dioxide in light of material balance when glucose undergoes the bio-fermentation, it is fundamentally inefficient
For the above reason, n-butanol has attracted attention as an alternative to ethanol. As compared with ethanol, n-butanol has high energy content and is lowly hygroscopic. However, new glucose fermentation is required, and researches for developing this are in progress.
To solve the foregoing problems, there is a furan-based compound such as 2,5-dimethylfuran (DMF) and 5-ethoxymethyl-2-furfural (EMF), called next-generation bio fuel that has attracted attention as another alternative using the carbohydrate-based biomass. Such a furan-based compound is excellent in energy content, is very lowly hygroscopic because of having no hydroxyl group as opposed to alcohols, and produces a little exhaust gas, thereby drawing interest.
Specifically, a general manufacturing method of deriving a desired final compound from a source of the carbohydrate-based biomass requires multistage processes of (a) the pretreatment for obtaining polysaccharide substance such as the starch, sugar and cellulose, (b) the saccharification for obtaining glucose or fructose, and (c) the bio-fermentation or catalysis-chemical process for obtaining the final compound. However, there is a problem of lowering a yield while experiencing the multistage processes.
Meanwhile, to employ the furan-based compound derived from the carbohydrate-based biomass as the petroleum-alternative fuel, a method of mass-producing a key intermediate platform material, 5-hydroxymethyl-2-furfural (HMF) shown in the following structural formulas has been being actively researched, in which HMF can be widely used as not only fuel materials but also a plastic monomer and an environment-friendly fine chemistry product such as an adhesive, a sticking agent, a coating material, etc. through various conversion reactions.

Hitherto, attempts to obtain HMF have been made by using the starting material of fructose mainly derived from the crop-based biomass supply source. This is because HMF can be relatively easily obtained from hexose such as fructose chemically having a pentagonal ring structure by only dehydration under an acid catalyst without separate isomerization.

Representatively, the Dumesic group has made researches on enhancing a yield and selectivity by separating a product from reaction a mixture under a biphasic condition and thus developed technology of obtaining HMF with a conversion rate of 90% from fructose (Yuriy Roman-Leshkov, Juben N. Chheda, James A. Dumeic, Science, 2006, 312, 1933-1937). H. E. van Dam et al. has proposed a method of obtaining HMF from fructose using p-toluenesulfonic acid as a catalyst (H. E. van Dam, Dr. A. P. G. Kieboom, Prof. H. van Bekkum, Delft University of Technology, Laboratory of Organic Chemistry, Starch, 2006, Volume 38 Issue 3, Pages 95-101). Also, the Zhang group of PNNL has obtained HMF with a conversion rate of 83% from glucose using a chrome catalyst in ionic liquid, in which glucose more usually exists than fructose but has a low conversion rate because of chemically having a hexagonal ring structure (Haibo Zhao, Johnathan E. Holladay, Heather Brown, Z. Conrad Zhang, Science, 2007, 316, 1597-1600).
However, fructose, glucose or the like exists in only some limited supply sources such as sugar cane, corn, etc., or it is impossible to economically extract fructose, glucose or the like from such sources. Therefore, it is difficult to mass-produce fructose, glucose or the like. Like this, the bio fuel produced from the crop-based supply sources such as sugar cane, corn, etc. uses food resources and thus shares the arable land with the food resources, so that the international grain price can be raised and cropping costs tend to interlock with the oil prices, thereby entering into international dispute.
To solve these problems, interest in the lignocellulosic biomass is increasing since it uses lumber sharing no arable land with a crop, wood wastes from municipal wastes, or forestry byproducts scattering in everywhere of a forest as a raw material and can be massively supplied. However, in the case of the lignocellulosic biomass, it is difficult to efficiently separate and remove solid lignin occupying about 30% of the contents in the pretreatment, and there is a need of many researches on application of lignin wastes. Further, the starting material of the lignocellulosic biomass, i.e., cellulose is more physically and chemically stable than those of the crop-based biomass, i.e., starch or sugar, so that the conversion process thereof has a high level of difficulty.
Recently, Mascal et al. and Joseph et al. have succeeded in a reaction of converting 5-chloromethyl-2-furfural (CMF), i.e., a precursor of the next-generation fuel EMF from cellulose at a high yield of 75% or more, thereby increasing the possibility of massively producing EMF from the lignocellulosic biomass [Mascal, M.; Nikinin, E. B., Angew. Chem. Int. Ed. 2008, 47, 7924-7926; Joseph B. Binder et al., J. Am. Chem. Soc., 2009, 131(5), 1979-1985].
Nevertheless, hydrochloric acid having a devastating effect on an engine is produced as a byproduct in the process of etherealizing CMF, and is blocking the massive production.
To solve the above-mentioned problems, marine resources have come into the spotlight as the third-generation biomass. The marine resources such as marine algae or the like maritime plants have a large allowable aquaculture area, have little effect of advance on costs based on use of fresh water, a land, a fertilizer, etc., and have high production per unit area because their growth ability is higher than that of land plants. Also, the marine resources contain no irremovable ingredient such as lignin, thereby facilitating the pretreatment. Further, the marine resources are superior to the land plants with respect to CO2 removal performance, thereby reducing greenhouse gas. Accordingly, development of conversion technology that produces bio fuel by employing marine biomass resources as a new supply source will be expected to carry an important meaning in an oil-free age.
Hitherto, the researches on the marine biomass have dealt mainly with a method of extracting triglycerides from microalgae and then converting it into fatty acid ester-based bio diesel through transesterification. However, it is hard to cultivate the microalgae in the maritime areas, and there is difficulty in a filtering process or the like.